16 



(lEOLOOY Olj' 'IIIK AVON ISASIN. 



of vegetal life, this too is ultimately determined in no 

 slight degree by geologieal structure. 



Not to go beyond the bare elements of scenery, however, 

 with which ahino 1 am hero directly concerned, lot mo 

 remind the observer of this fact, that the physical features 

 of our district are partly produced, and 'partly reproduced, by 

 the denudation at present in progress. The Clifton-Clcvedon 

 ridge, the Portishead-Clevedon ridge, like the " Westbury 

 Horseshoe," Backwell Down, and tlie Mendips, are old 

 scenic features which wei'e in existence, perhaps more 

 markedly than now, in pre-Mesozoic times. Upon the 

 upturned and denuded edges of the strata of which they 

 are formed were laid down the Dolomitic Conglomerate, 

 Trias marl. Lias, and Oolitic rocks. It has been the work 

 of latter-day denudation to remove to a very largo extent 

 this thick Mesozoio cover, and having done so to proceed to 

 I'ofashion and carve afresh the old features produced by the 

 pre-Mesozoic denudation. How far such physical features 

 as the Lower Limestone Shales depression and the soft and 

 open valleys of the lower beds of Old Red Sandstone are the 

 product of modern denudation, or the survival of the de- 

 nudation of a by-gono ago, it is impossible to say foi' certain. 

 But it is my own belief that these features are modern modi- 

 fications of the old rough-hewn model, and a,rc, in their 

 present form, the outcome of the sandpaper action of modern 

 frost and rain, and the file-like action of the present brooks 

 and streams. 



